This invention relates generally to the field of gauging the tolerance of the positions of holes punched in material such as punched computer cards or paper tape and more particularly to an apparatus for automatically gauging the tolerance of the positions of individual holes punched in a continuous, moving web of material.
Many devices rely upon input information from punched cards or paper tape, for their operation. This information may be data to be processed by a computer or commands to control its operation or the operating parameters for some device. This information is provided by the position and format of the holes which are punched in the material. In many applications, it is essential to insure that the positions of these punched holes are held within certain tolerances in order prevent reading devices from misinterpreting the information. This is particularly true of electronic devices which derive their operating parameters from one or more punched cards, which are inserted in stationary readers, comprising a plurality of electrical contacts arranged in a pair of matrices, which are brought into contact with the punched card inserted between them.
The holes punched in the cards permit certain of the electrical contacts on one of the matrices to mate with corresponding contacts on the other matrix, thereby completing electrical circuits. The positions of the holes punched in the card determine which circuits are completed, and therefore what information is supplied to the device. Due to the large number and close spacings of the electrical contacts utilized in such matrices, slight misalignments of the positions of holes punched in the card may permit undesired electrical connections to exist, thereby providing erroneous information to the device. Similar problems exist with respect to card readers and paper tape readers, which read the information from punched cards or paper tape as it is passed across some sensing mechanism.
Occasionally, the mechanical punches utilized to punch the holes in such cards or tapes can become misaligned or out of tolerance due to mechanical wear. Furthermore, some cards are punched using two or more longitudinally staggered punches. These may become misaligned with respect to one another or the mechanism which steps the card from one punch to another may produce inexact stepping. Consequently, punched material must be gauged to insure that the positions of the holes that are punched therein are held within predetermined tolerances.
Previously available gauges have usually taken the form of a template of an accurately punched formatted section of material, over which is manually positioned a section of punched material. The material is then visually inspected for any misalignment of the punched holes with respect to the gauge. This method has the disadvantage of being slow and unreliable when gauging large quantities of material.
Another widely used technique is to verify that the data actually punched in cards is correct. Typically, this is accomplished by comparing the data actually punched in the cards with the data that was input via the keyboard of the keypunch. For example, see U.S. Pat. No. 3,596,831 to Parmer and U.S. Pat. No. 3,765,603 to Bean. These techniques have the disadvantage of requiring elaborate circuitry to store the data keyed into the keypunch, readers for the cards, and other circuitry to compare the date punched in the card with that keyed into the keypunch.
Systems which perform dimensional verification of punched cards or paper tape are typified by U.S. Pat. Nos. 3,684,164 to Davis and 3,558,862 to McMillan. The former reference discloses a system in which photocells are spaced from the punch by a distance equal to the column-to-column spacing on a punched card. As each column is punched and the card is advanced to the point where the next column is to be punched, the previously punched column of holes is aligned with the photocells. A light source illuminates one or more of the photocells through the punched holes to provide an output indication that the card has advanced the proper distance, and the punch is permitted to operate to punch the next column. Otherwise the machine is halted.
The latter reference (McMillan) discloses a system which utilizes the sprocket holes in a punched paper tape to determine the column-to-column spacing of punched data. As the tape is pulled across a photocell at a constant speed, the photocell is illuminated as each sprocket hole passes over its position. The photocell output is utilized to gate a constant frequency pulse source to a counter. By counting the number of pulses between holes, the distance between them is determined. As long as the number of pulses between holes falls within predetermined limits, an in-tolerance condition is indicated.
Both of these techniques suffer from the disadvantage that they perform gauging in only one dimension, i.e. longitudinally. Furthermore, gauging of individual holes is not performed. Rather, it is assumed that all holes in a column are perfectly aligned and only the column-to-column spacing is gauged.
There exists a need to quickly, efficiently and accurately gauge, in two dimensions, individual hole positions in large quantities of punched cards and paper tape. It is to this end that the present invention is directed.